Can Liouville's number be expressed as a physical ratio in the sense that $\pi$ is? - MathOverflow most recent 30 from http://mathoverflow.net 2013-05-26T01:46:52Z http://mathoverflow.net/feeds/question/116755 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/116755/can-liouvilles-number-be-expressed-as-a-physical-ratio-in-the-sense-that-pi-i Can Liouville's number be expressed as a physical ratio in the sense that $\pi$ is? intuilog 2012-12-19T04:39:28Z 2012-12-20T05:33:07Z <p>Quadratic irrational numbers are perhaps the most basic examples of irrational numbers that arise as basic physical ratios: think of $\sqrt{2}$ as the distance between the corners of a square to the length of a side for example.</p> <p>Similarly, the number $\pi$ is the ratio of the circumference of a circle to its diameter. Even $e$ can be realized in this sense as the distance $a$ such that $\int_{1}^{a}\frac{1}{x}dx=1$. Are there similar understandings for other irrationals?</p> <blockquote> <p>Can Liouville's number be expressed as the ratio of two measurements of a geometrical object?</p> </blockquote> <p>I will add my inspiration for asking this question in the hopes of encouraging more discussion that can help me focus these ideas. While pondering the argument for the existence of two irrational numbers $a$ and $b$ such that $a^b$ is rational using $\sqrt{2}^\sqrt{2}$ and the "<a href="http://en.wikipedia.org/wiki/Law_of_excluded_middle" rel="nofollow">law of the excluded middle</a>", I wondered at the linked wikipedia article's note that an "intuitionist" would not accept this argument as proof. I feel like the only way to reject this argument as proof would be to question the assumption that $\sqrt{2}^\sqrt{2}$ exists as a real number, and in fact must be either rational, or irrational. (Any intuitionists want to way in?)</p> <p>This led me to ask myself, how do I know that $\sqrt{2}$ exists? I of course immediately answered that it was the ratio of the diagonal of a square to the length of a side! This led me to consider the "existence" of other irrational numbers as "some sort" of "physical ratio."</p> <p>In considering this I would (for now) accept the description of $e$ above as being a "physical ratio."</p> <p>Can anyone help me define what I mean by these "physical ratios?" I suppose I am looking for some argument for the "existence" of otherwise incomprehensible numbers, and whether or not every irrational could be explained in such a way.</p> <p>I of course must note that this is incredibly vague and that the only one who can truly decide what I mean is myself, but any advice would be great!</p> http://mathoverflow.net/questions/116755/can-liouvilles-number-be-expressed-as-a-physical-ratio-in-the-sense-that-pi-i/116767#116767 Answer by ACL for Can Liouville's number be expressed as a physical ratio in the sense that $\pi$ is? ACL 2012-12-19T08:08:39Z 2012-12-19T08:25:39Z <p>The answer is probably <em>no</em>.</p> <p>In his paper <a href="http://www.math.jussieu.fr/~miw/articles/pdf/TranscendencePeriods.pdf" rel="nofollow">Transcendence of Periods: the State of the Art</a> (Pure and Applied Mathematics Quarterly, Volume 2, Number 2, p. 435-463, 2006), Michel Waldschmidt conjectures that no period is a Liouville number (see questions 2 &amp; 3 in the introduction). This expectation is supported by the main advances of transcendental number theory in 20th century, notably Baker's theory of linear forms in logarithms and its extensions to commutative algebraic groups.</p> <p>Here, the word <em>period</em> has to be understood in the sense of Kontsevich and Zagier: a complex number whose real and imaginary parts are values of absolutely convergent integral of rational functions with rational coeﬃcients, over domains in $\mathbf R$ given by polynomial inequalities with rational coeﬃcients. (The preceding definition is quoted from the paper <a href="http://arxiv.org/abs/0805.0349" rel="nofollow">Periods and elementary real numbers</a> by Masahiko Yoshinaga, who was apparently the first to prove that periods belong to the field of elementary complex numbers, those whose real and imaginary parts can be effectively approximated by Cauchy sequences of rationals.)</p>